An experimental study on clear water temporal scour around eccentric circular piers

Abstract

One possible reason for bridge failure has been identified as scour near the piers. Increasing traffic load in an urban area leads to the construction of a new bridge beside the existing one. This type of parallel bridges create situations like tandem and eccentric pier combinations. The literature study confirms that there was much attention given to the work that delves into creating techniques to forecast the depth of scour as well as to understand the dynamics underlying scour only around the single pier. There was limited research found on the eccentric anangement of piers in clear water conditions. Therefore, in the present study, an attempt has been made to understand how scour depth changes with time, and the effect on maximum scour depth with respect to different flow parameters such as flow intensity, flow shallowness and Froude number. In the present study, a total of 24 experiments were conducted with fixed discharge of 20 Ips and longitudinal spacing of 5.19b where b is the pier diameter, and with six different eccentrics spacings (26-3.5b) as well as with four different flow intensitics (0.67-0.97), Froude number (0.20-0.32) and flow shallowness (1.2-1.65). Το compare the maximum scour depth around eccentric pier arrangements, four additional single-pier experiments were carried out. The dimensional analysis has been performed to ensure the influential parameters which influence the temporal scour depth. The geometry of scour profiles has been analysed, whether the eccentric-piers arrangement causes a symmetric or non-symmetric scour. If it is not symmetrical, the greater scour is determined on which side of the pier it is shifting. The scour width and the total scour length have been analysed how they affect the sediment shifting process at the downstream of the eccentric pier. The temporal evaluation of the scour depth has been analysed to check the quasi-equilibrium state of the scour. The separate effects of flow intensity, Froude number, time, and flow shallowness on scour depth have been analyzed. Dimensionless analysis reveals that flow shallowness, flow intensity, Froude number, dimensionless time, and dimensionless lateral spacing are the key parameters influencing the scour depth around both front piers and eccentric piers in the current experimental data set. The maximum and minimum scour depth for front and eccentric piers are found to correspond to the maximum value of flow intensity, Froude number, dimensionless time and minimum value of flow shallowness and vice versa. When all of the eccentric pier arrangements are analyzed, it becomes clear that the left portion of the front pier has the maximum and minimum scour length, while the right and left sections have the maximum and minimum scour width. Additionally, it was identified that the left section has the least planar surface area and scour volume, while the right section has the maximum. From an overall perspective, it can be stated that when eccentricity increases, sediment deposition spreads in the right section of the eccentric pier with respect to the flow direction, and when eccentricity decreases, the same things occur on the left side of the front pier. This study may help to select criteria that minimize scour is essential for constructing bridge piers safely and cost-effectively. Maximize scour, which is also necessary for these arrangements, by shifting sediment to one side of the riverbank, which can aid in navigation and be beneficial for protecting the riverbank. For the self-dredging phenomenon, shifting sediment on one side of the bank is also beneficial.